GHC comes with a rather large collection of type-system extensions (beyond Haskell 98). They are all documented in the [http://www.haskell.org/ghc/docs/latest/html/users_guide/type-extensions.html user manual], but this page is a place to record observations, notes, and suggestions on them.

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GHC comes with a rather large collection of type-system extensions (beyond Haskell 98). They are all documented in the [http://www.haskell.org/ghc/docs/latest/html/users_guide/ghc-language-features.html user manual], but this page is a place to record user-oriented observations, notes, and suggestions on how to use them.

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== Overlapping instances ==

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* '''[[GHC/Indexed_types|Indexed data types]]'''

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* '''[[GHC/TypeHoles|Agda-like "holes" in GHC]]'''

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Here an [http://www.haskell.org//pipermail/glasgow-haskell-bugs/2006-July/006808.html interesting message] about the interaction of existential types and overlapping instances.

* '''Overlapping instances'''. GHC supports overlapping instances, with carefully specified rules. Make sure you read the [http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#instance-decls relevant sections of the user manual]. Here is an appliation note about [[GHC/AdvancedOverlap|advanced use of overlapping instances]], combined with functional dependencies.

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* '''[[GHC/Coercible|Safe coercions using Coercible]]'''

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[[GHC/Indexed_types|Indexed data types]] (including associated data types) are a very recent addition to GHC's type system extensions that is not yet included in the user manual. To use the extension, you need to obtain a version of GHC from [http://hackage.haskell.org/trac/ghc/wiki/Building/GettingTheSources its source repository].

Latest revision as of 08:57, 20 May 2014

Type system extensions in GHC

GHC comes with a rather large collection of type-system extensions (beyond Haskell 98). They are all documented in the user manual, but this page is a place to record user-oriented observations, notes, and suggestions on how to use them.